diff --git a/src/compiler.rs b/src/compiler.rs
index b615785..39e3c27 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -339,41 +339,26 @@ impl Context {
         *self.get_mut('t')? += 1f64 / (SAMPLE_RATE as f64);
         *self = self.slopes.iter().try_fold(
             self.clone(),
-            |mut acc,
-             (
-                v,
-                Expression {
-                    from: _,
-                    instruction,
-                    slab,
-                },
-            )|
-             -> Result<Self, CompilerError> {
-                *acc.get_mut(*v)? = instruction.eval(
-                    slab,
-                    &mut acc
-                        .variables
-                        .iter()
-                        .map(|(c, f)| (c.to_string(), *f))
-                        .collect::<BTreeMap<String, f64>>(),
-                )?;
+            |mut acc, (v, e)| -> Result<Self, CompilerError> {
+                *acc.get_mut(*v)? = acc.eval(e)?;
                 Ok(acc)
             },
         )?;
         Ok(())
     }
 
-    fn namespace_generator(&self) -> BTreeMap<String, f64> {
-        self.variables
-            .iter()
-            .map(|(c, f)| (c.to_string(), *f))
-            .collect()
+    fn namespace_generator(&self) -> impl Iterator<Item = (String, f64)> {
+        self.variables.iter().map(|(c, f)| (c.to_string(), *f))
     }
 
     pub fn eval(&self, expr: &Expression) -> Result<f64, fasteval::Error> {
-        self.eval_with(expr, &mut self.namespace_generator())
+        self.eval_with(
+            expr,
+            &mut self.namespace_generator().collect::<BTreeMap<_, _>>(),
+        )
     }
 
+    #[cfg(not(test))]
     pub fn eval_with(
         &self,
         Expression {
@@ -386,15 +371,34 @@ impl Context {
         instruction.eval(slab, ns)
     }
 
+    #[cfg(test)]
+    pub fn eval_with(
+        &self,
+        Expression {
+            from,
+            instruction,
+            slab,
+        }: &Expression,
+        ns: &mut (impl EvalNamespace + Debug),
+    ) -> Result<f64, fasteval::Error> {
+        let result = instruction.eval(slab, ns)?;
+        println!("expression {from}\twith values {ns:?}\t equals {result}");
+        Ok(result)
+    }
+
     pub fn render(&mut self, n: Option<u8>) -> Result<Vec<f64>, CompilerError> {
         let curr_t = *self.get('t')?;
         if let Some(note) = n {
             let mut result = Vec::new();
-            let mut map = self.namespace_generator();
+            let mut map = self.namespace_generator().collect::<BTreeMap<_, _>>();
             map.insert('n'.to_string(), note as f64);
             while self.current_length()? > *self.get('t')? - curr_t + (1f64 / SAMPLE_RATE as f64) {
                 result.push(self.eval_with(&self.instrument, &mut map)?);
                 self.tick()?;
+                map = self.namespace_generator().fold(map, |mut acc, (k, v)| {
+                    acc.insert(k, v);
+                    acc
+                })
             }
             Ok(result)
         } else {